Drum type induction furnace



March 7, 1950 M. TAMA DRUM TYPE INDUCTION FURNACE 4 Sheets-Sheet 1 Filed Aug. 29, 1947 March 7, 1950 M TAMA 2,499,541

DRUM TYPE INDUCTION FURNACE Filed Aug. 29, 1947 4 Sheets-Sheet 2 @fly 4 IN VEN TOR. MR/0 THW/A7 March 7, 1950 M. TAMA DRUM TYPE INDUCTION FURNACE Filed Aug. 29. 1947 4 Sheets-Sheet 3 IN V EN TOR. MR/0 THM/ March 7, 1950 M. TAMA 2,499,541

DRUM TYPE INDUCTION FURNACE Filed Aug. 29, 1947 4 Sheets-Sheet 4 IN VEN TOR. MAP/0 WIM/l Patented Mar. 7, -1950 DRUM TYPE INDUCTION FUR/NACE Mario Tama., Morrisville, Pa., assignor to Ajax Engineering Corporation, Trenton, N. J.

Applieation August 29, 1947, Serial No. 771,360

This invention relates to a drum type induction furnace for melting heavy and light metals and their alloys; it refers more particularly to an induction furnace in which the inductor units are located at the periphery or circumference of a. metal holding drum and beneath its horizontal center plane. The invention represents a further development of the drum type induetion furnace disclosed in the inventors U. S. Patent No. 2,474,443.

The term inductor unit wherever used in this specification is deemed to describe that part of the inductor furnace where the heat is generated.

This inductor unit consists of a metallic refractory-lined casing housing the secondary loop, a transformer assembly threading the secondary loop, and at least one blower or other suitable means for cooling the primary coil. When current is caused to flow through the primary winding of the transformer assembly a heavy current is induced in the secondary loop, thus generating-the heat which melts the metal charged into the metal holding space of the furnace. The inductor unit being a separate self-contained part of the furnace is one of the principal features of the present invention.

The terms "drum furnace or drum type furnace are to be understood in their broadest sense o r import. They are not limited to signify a cylindrical-shaped*melting vessel, but are deemed to include any metal holding space or hearth of Vsubstantially uniform cross section capable of being rotated around a horizontal axis thereof.

It has been hitherto customary to attach one or more inductor units or a row of inductor units tothese furnaces and it is also known to make these inductor units removable, see for example U. S. Patent No. 2,102,582.

The invention represents a vital step in the further development of these drum type induction furnaces, because it increases their applicability in a most satisfactory manner as will become apparent from its hereunder stated diversiiled ramifications.

It is an important object of the invention to concentrate a large amount of power and consequently to effect a more intensive melting in a restricted furnace space.

Another essential object of the invention is to I satisfactorily melt in drum-type induction furnaces metals which have the tendency to form oxides and dross layers on the surface of the molten bath; the instant furnace is particularly well adapted to .melt zinc cathodes, brass and 67 Claims. (Cl. 13--29) allnninum turnings, chips, scalpings and similar metallic materials which were considered difficult and even impossible to handle in the customary drum type induction furnaces.

It is another object of this invention to simplify the exchange of inductor units and to shorten the time required therefor; at the same time the novel construction of the present drum-type inductor furnace renders it possible to continue the operation of the furnace and to maintain a substantial percentage of its working efficiency while an inductor' unit is replaced.

It is also an object of this invention to effect the discharge of the molten metal from a large range of levels.

It is another advantage of the invention to obtain uniform metal melts.

Another important object of the invention is to facilitate the connection of an induction furnace to a three-phase power supply. Since the number of inductor units is preferably three or a multiple of three it will always be possible to balance the power supply by connecting three units in delta or star or as hereunder called triad arrangement to the three cables of the power line.

It is another essential object of the invention to prevent the accumulation of slag deposits in the melting channels of the inductor units and to eliminate the clogging thereof, thereby greatly reducing the necessity for their replacement or exchange; in this respect the instant furnace shows a decided improvement over the art, be-

cause it permits the cleaning of the melting channels from the outside of the furnace without interrupting the melting even while an inductor unit is being exchanged.

It is an equally important object of the invention to improve and to intensify the circulation of the molten charge through the entire melting space and to prevent local overheating thereof.

With these and other objects in view which will become apparent as this specification proceeds, the furnace will now be described in several preferred embodiments which are illustrated in the attached drawings. However, it is to be understood that the invention is not restricted to the modifications described and shown.

The drawings illustrate three furnaces which have proven to be particularly well adapted for carrying out this invention:

In the drawings,

Fig. i is a vertical sectional view of a drum- 3 type furnace representing a first embodiment of this invention. i

Fig. 2 is a vertical sectional view on line 2-2 of Fig. 1,

Fig. 3 is a partly broken right end view of the furnace shown in Fig. 1, l

Figs. 4, 5, 6 are schematic side end views of the furnace in various tilting positions, looking from the end of the drum where the hydraulic cylinders are located,

Figs. 7 and 8 are sectional views similar to that of Fig. 2 showing the furnace in its various posie tions for the exchange of the inductor units,

Fig. 9 is a vertical sectional view similar to Fig. 1 of a second embodiment of the furnace,

Fig.Y 10 is a vertical sectional view on line lll-i@ of Fig. 9,

Fig. l1 is a vertical sectional view of a third l embodiment of the furnace,

Fig. 12 is a vertical sectional view on line i2l2 of Fig. 1l.

As apparent from Fig. 1 and Fig. 2, the furnace is provided with a drum-shaped or cylindrical casing i, protected by a refractory lining 2; the casing houses a horizontal hearth 3; it has attached to its periphery three rows of induetor units l, 5 and 6. The normal working position of the furnace corresponds to the one shown in these Figures l and 2.

The furnace has a`top opening which is closed by a removable cover l. The furnace drum is provided at'both ends with circular tracks 8 resting on roller bearing supported wheels 9 which are mounted on a base it; rollers 9B are provided to prevent the longitudinal displacement of the drum.

A characterizing feature of the furnace is the novel arrangement of the inductor units which in the present modification of the invention are represented by three rows consisting each of two longitudinally alined units; however, the number of the inductor units in the individual rows is by no means limited.

These units are so located that the melting loops of the center or bottom units 5 extend in the normal working position of the furnace through its vertical center plane whereas the melting loops of the lateral inductor unit rows d, 6 extend through planes which form acute angles with the vertical center plane of the furnace.

As previously stated, single inductor units are provided in a number which is 3 or amuitiple of .3. In the present embodiment of the invention one row of two longitudinally alined inductor units 5 extend through the vertical center plane of the furnace whereas two rows consisting of two inductor units 4 and 6 are symmetrically arranged on both sides of the center row.y The installation of more and particularly three inductor units or inductor unit rows, of which one unit or row of units is located in the vertical longitudinal center plane of the furnace and designated in the following as triad inductor arrangement is a prominent feature of the inven tion and has important advantages.

First of all a high concentration of power is`- hereby established in a restricted or small space encountering the hitherto customary drawbacks of this procedure; this is a most desirable accomplishment of this invention, because a high melting efficiency is accordingly obtained in this restricted space. Such concentrations of power has hitherto had its early limits and could not be successfully utilized in drum-type induction furnaces because ofthe insuflicient metal movement within and from the Inductor units, which resulted into an unsatisfactory heat distribution.

Therefore the installation of melting loops according to the invention adapted to create a strong circulation of the molten metal and therewith an intensified heat distribution within a restricted working space of high power concentration is a characterizing feature of the instant drum-type furnace. Melting loops of the twin coil type as, for instance, shown in applicants Reissue'Patent No. 22,602 patented February 13, 1945 greatly improve the eiciency of drum type inductor furnaces and ndin connection with the same anunexpectedly satisfactory field of application. Particularly adapted to use with this invention are the inductor units disclosed inapplicants copending U. S. application Serial No. '735,851 iled February 20, 1947 which not only produce an intensified but in addition thereto a unidirectional metal flow. The increase of the number of inductor units or inductor unit rows therefore reaches a maximum of working eniciency if combined' with inductor units adapted to produce an intense and particularly an intense unidirectional metal circulation in and from the inductor units. If the metal movement towards and from the melting channels of the inductor units is sluggish the transfer of heat from the same to the restricted working space of a drum type furnace would not suflice for the high load and the furnace could not function properly.

By preferably using three inductor units or inductor unit rows it is possible to well balance the load in a three phase power supply.

This very disadvantageous requirement is eliminated by the invention since it is easy to connect each inductor to each phase of the power supply and to thereby obtain a complete balance of load. Each unit can .be controlled separately.

Finally, by the use of three or more inductor units or rowsthereof,` it is possible to intensify the movement over the entire surface of the metal bath. in particular, the lateral inductor units produce a desirable turbulence on the two sides of the drum, while the center unit or units keep the bottom portions in a steady motion. High melting emciency and a thorough moving of the melt are the results of this novel inductor arrangement.

In conformity with the above each melting loop consists of a melting channel i2 which is spaced from the hearth t and preferably extends parallel to the longitudinal direction of the drum anis, and three straight channels i3, i6, ,l5 connecting channel l2 with the hearth. The melting channels are in the customary manner threaded by transformer units comprising coils i6 of insulated copper wire and an iron core il closed toward the coil windings. The cooling blowers i Q are attachable to the inductor units. They serve to remove the heat from the primary winding.

In view of the known construction of these inductor units a more detailed descriptionl thereof is omitted. They are housed in refractory lined f casings l'l which are removably attached to the drum casing i in the manner as for instance shown in a pending U. S. application filed jointly :by applicant and Manuel Tama Ser. N o. 632,898

filed December 5, 1945, now Patent No. 2,423,912,

issued July 15, 1947; they may be removed by loosening bolts, not shown, which connect the drum casing i and the inductor casings Il along a horizontal plane 36.

The furnace can be lled in its normal position 75 shown in Figures 1 and 2 up to'level 88a. The

inclination of the lateral inductor units l, 6 may be preferably chosen in such a manner that the center lines 24 of all melting channels located in the same plane converge at a. point 20 above the geometrical center 2I of the furnace, see Fig. 2. In the extension of the center lines 24 openings 22 are provided in the drum cover through which cleaning tools can be introduced into the channels while the same are full with the molten metal. An inclination of about 45 degrees of the laterali melting loops relative to the center or' bottom melting loop has proven to be particularly advantageous; the melting channels having this inclination can be cleaned without emptying the furnace.

Another important feature of the invention is the easy replacement of worn-out inductorunits without interrupting the working of the furnace. The exchange of inductor units is performed after rotating the furnace to a position where the melting loop of the unit to be replaced has reached approximately the horizontal center plane of the furnace and the molten metal has. been discharged from its melting channels into the hearth.

The rotation of the furnace is achieved by means of a double acting hydraulic cylinder 23 shown in Figures 4, 5, 6, which is rotatably mounted on base IIl, by means of bolt 63 and ears '25; the piston 26 of the cylinder is connected with lever 21 which is rotatable around the center 2I of the furnace and attached to the furnace drum. A small hydraulic cylinder 28 is provided to hold the furnace drum in place in its various tilting positions shown in Figs. 4, 5, and 6.

The normal working position of the furnace corresponds to the one shown in Figs. 1 and 2. For the exchange of a lateral inductor unit the furnace must be tilted from the position of Fig. 2 into the one shown in Fig. 7 whereby a corresponding portion of the metal is discharged-from the hearth through opening 6I. This is also the position where a lateral inductor unit 6 may be emptied into the hearth and can then be detached from the casing I for replacement, while the other four units continue to heat the metal contained in the drum. If it is desired to exchange a bottom inductor unit 5, the furnace is tilted into the position `shown in Fig. 8; to exchange another lateral unit 4 the furnace is rotated in the opposite direction. During the rotation of the furnace and during. the replacement of an inductor unit, the furnace can be maintained in operation with the residual units.

Afterv a bottom induction unit 5 has been replacedthefurnace is gradually rotated back into its normal position and a new charge of molten metal is built up by adding fresh metal into the induction units which have been kept in operation. When sufficient material has been accumulated in the drum it will be easy to nil the center unit or units by further rotation. At this point two units or rows of units are again in full operation and more metal can be charged to fill the last inductor unit or units.

The same procedure can be followed for starting the furnace for the first time.

'I'he priming position is that shown in Fig. 8. With the drum almost completely tilted, the hearth and the inductor units are well preheated by an external heating source, for instance, with a suitable number of gas or oil torches. Thereafter molten metal is introduced into the two lateral inductor units 6 shown in the lowest position in Fig. 8. These two units can now be started working by switching the power on and they will immediately commence to heat the metal in the units and in the adjacent section of the hearth. Thereafter the furnace is gradually turned back into the normal position, a bed of molten metal is built up and the procedure is the same as described above.

In any way it is possible to keep always at least one unit or one row of units filled and under power and to thereby keep the furnace hot during the replacement of inductor units; which is important as it prevents the cooling of `the refractory lining.

Cover 1 consists of four individual liftable sections 29; only one of these sections needs to be lifted in order to charge the furnace.

Metal is discharged from the drum over opening 6I connected with a discharge pipe 30 made preferably of cast iron and provided with a refractory lining 3 I. By tilting the furnace, molten metal can be taken out gradually under full control of the pouring speed. The furnace reaches its full level in the position shown in Fig. 2. From there on molten metal can be discharged over pipe 30 until the position of Fig. '7 is reached. which indicates the working limit of pipe 3D; further tilting would be of no avail. It additional metal is to be discharged another opening 6l) located in a side-wall of the furnace has to be used. This opening is ordinarily closed by a refractory plug; molten metal can be discharged through opening 6I! until the level I8b is reached, which is shown in Fig. 8. If a complete discharge of the furnace is desired, the inductor units located at the. lowest load in Fig. 8 can be emptied in a known manner by opening the plugs 52, Figi.

It is apparent from the above that it is possible to widely vary the emptying degree and to completely empty the furnace, an operation which was very difficult to perform with existing drumtype induction furnaces.

A door 32 is provided which facilitates the removal of slags from the surface of the bath. One or more of the cover sections should be removed before the slags are pushed-out through this door opening.

In the embodiment of the invention illustrated in Figs. 9 and 10 similar parts of the furnace are designated with the same numerals; also here the drum type induction furnace is provided with three inductor units k4, 5, 6; as in the rst embodiment, the melting loop of the center or bottom unit 5 extends through the vertical center plane of the drum casing I and the melting loops of the symmetrically located lateral units 5, E form acute angles with the vertical center plane of the furnace.

This modification of the invention is designed with the particular purpose to melt oxide containing charges such as zinc cathodes or any other metals which have a tendency to form thick oxidic layers on the surface. The furnace is provided with a large uncovered top opening 33 for the charging of fresh metal into hearth 3. The melting loop is of the previously described twin coil type having a channel II spaced from the hearth and three lateral channels I3, I4, I5 connecting channel II with the hearth. The inductor units are made detachable from the drum casing in the previously described manner. Also the rotating mechanism is the same. In the ordinary operation of the furnace the metal level will vary between level I8 and a plane extending through the geometrical center 2I of the furnace.

'I'he furnace diilers from that previously shownA in the following respects:

Tubes 35 made of a current conducting refractory material such as graphite, carbon or carborundum inserted into center channels N of the melting loops extend through the refractory lining 2 of the drum casing and open into hearth 3. The refractory lining of the inductor unit is recessed at 36; therefore, tube 35 is for a certain length still under the influence of the magnetic field of the transformer units, because a current flows through its walls. At the exit end oi tube 35 into hearth 3 a circular protective brick il is provided in the lining 2 of the drum casing.

In the direction of the lateral channels i3, i passages 38 are provided in` the refractory lining 2 of the drum. They are downwardly enlared and connect the hearth with the upper ends of the lateral channels. Due to the extension oi melting channel i4 by means of tube 35 into a section of the hearth which is practically free from the influence of the magnetic field created by the transformer units the same unidirectional ow of the molten metal is obtained, which has been disclosed in applicants copending U. S. applications Serial Nos. 735,851 led February 20, i947, and 755,886 led June 20, 1947. The thus extended flow impulse of the melt reaches far into .the upper and center portions of the drum and forces the upwardly directed metal stream to return in an opposite direction through the lateral melting channels i3, i5. The metal is therefore upwardly discharged from channel lil and tube 35 in the direction of arrows 3d and consequently must ilow at all times in an opposite direction from the hearth along arrows d through channels I3, i5 and from there return into channel M. In this manner a constant one-way or unidirectional circulation of the metal through the inductor units and the hearth is obtained; the results are a thorough homogenization of the melt and a complete uniformity of temperature. In the center portion of the bath a comparatively movement-free quiet zone exists and accordingly the further important advantage results that oxides which are charged wit-h the fresh metal into the center of the hearth will not be conducted into the melting loop.

A further interesting improvement of this second embodiment of the invention resides in the i For this purpose a spigot is used which consists of a refractory body 4I, a discharge channel 42, having the shape of an inverted V with horizontal end portions 44a, Mb is provided in this body; the end portion Macommunicates with a horizontal discharge channel 43 in the side wall of the drum. The other horizontal end-portion Mb opens into a short vertical channel 45 which terminates beneath discharge channel 43. By means of this spigot the metal level in the hearth is gradually lowered when the drum is rotated until the horizontal center plane isl reached. The distance between the vortex of the V-shaped channel 42 and the discharge channel 45 is so dimensioned as to prevent the outow of the metal from the hearth inthe normal position of the furnace.

If the furnace is to be emptied beyond the cen ter plane another suitable opening 60 may be provided in the side wall of the drum.

A third embodiment oi" the invention is illustrated in Figs. 1l and 12, which resembles the second embodiment insofar as it is also provided 'with three mductcr units attached to the periphery of the drum casing beneath its horizontal center plane; also here similar elements of the furnace are designated with the same numerals. v

' The melting loop of the centerl unit 5 extends in the normal working position through the vertical center plane of the drum and the melting loops ci the two lateral symmetrically arranged inductor units 5, t through planes which form an acute angle with the vertical center plane. A mecha-n nism as previously described may also here be used to rotate the furnace in both directions and into its various positions for the discharge oi the metaland the replacement of the inductor units which need repair or are worn out.

In alinement with channels i8, ifi, i5 of the` inductor units passages Se, Sez .are provided in the refractory lining 2 oi casing i. Passages S3 are attheir lower ends enlarged to form recesses 552. The refractory lining oi casing i through which passage 3de leads ends short of center channel i6. A tube made oi current conductive refractory material such as graphite or carborundum connects passages 38d with center channels ii of the inductor units.

Also here the center lines of the inciting chan nels converge at points 2@ above the center line il of the drum which facilitates the cleaning of the melting channels from outside the furnace while the same are kept full of metal.

kThe main distinguishing feature of this ern bodiment of the invention from those previously described consists in the provision of the walls 5@ which extend through casing i; in this manv ner the inner drum or casing space is divided in a centrally located hearth and two lateral chambers 5&3. Passages d5 in the walls 5o cone neet hearth i and chambers lill and passages et connect the bottom portions ory the chambers with recesses 52 and therewith lateral melting channels i3 and i5 of each inductor unit. in this manner provisions are made for a continuous one-way or unidirectional flow of the metal from center channel itl through passage 38a' in the direction of arrows 3e, passages 55 lateral chambers 5d in the direction of arrows te, passages 55, recesses 52 into lateral channels i3, i5 and from there back into center channels i'l. By virtue of this structure the furnace is Darticularly adapted for the melting of metals which are apt to form oxides and dross.

The metals are charged into the hearth t I through opening 33 where a portion of the dross accumulates on the surface of the bath. Since the continuous unidirectional metal ow emerg-n ing from the center channel is prevents sucking of oxides into the melting circuit, the dross remains on the surface and does not clog'the melting channels.

A purified metal, free oi dross, flows into the lateral chambers 5t. Furthermore, as the metal in these chambers is protected against the movement of the bath, further puriiication is obtained by the upward floating of suspended oxidic impurities; a purer metal will therefore accumulate in the lateral chambers. The thus obtained purification of the metal is further enhanced be cause the charging section is completely separated from the metal discharge sections, as the metal is emptied from chambers dfi by spigot Si.

Moreover, by the charging of the metal into hearth 3 where the hot metal continuously emerges in the direction of arrows 39 into lateV eral chambers 54 a rapid interchange is obtained between the heat produced inthe melting loops and the charge. As there is no sucking action at the emergence of the'melting channels intol the hearth the danger of oxides being drawn into the melting channels -is eliminated. All oxidic impurities will accumulate on the surface of the bath; the dross accumulating on the bath in hearth 3 is removed from time to time over the lateral slopes 64 bordering opening 33.

The passages 38 are closed by plugs 59 which are only dislodged for the cleaning of the channels I3, l5 whereas the center channels can be directly reached by cleaning tools from above through passages 38a.

The description of the prior embodiments of the invention with regard to the rotation of the furnace, the discharge of the metal, the replacement of the inductor units and the cleaning of the melting channels also apply to the present embodiment.

In all the examples described in the present application, detachable inductor units are used for the purpose of obtaining continuous operation of the melting furnace. Otherwise it would be required to stop the operation of the furnace for cleaning the inductor units. With the use of detachable units it is only necessary to discontinue the operation for a few hours until the change is performed. Further details of the steps to be followed in performing the exchange of inductors are not given because they have been described in prior patents, for instance, in U. S. Patent No. 2,102,582.

Three embodiments of the invention are described and illustrated but it is to be understood. that any change of the devices shown may Vbe made within the scope of the following claimsy and without departure from the scope of this invention.

I claim:

1. In a drum type induction furnace particularly for melting metals a hearth, a refractorylined casing housing said hearth, a plurality of inductor units attached to the periphery of said casing below its horizontal center plane, secondary meltingloops in said inductor units operatively connected with said hearth, the melting loop of one of the said inductor units extending through the vertical center plane of the furnace and the melting loops of the other inductor units located at each side of said vertical center plane extending through a plane forming an acute angle with said vertical center plane.

2. In a drum type induction furnace particularly for melting metals turnable about its longitudinal center axis a hearth, a refractory-lined casing housing said hearth, a plurality of inductor units replaceably attached to the periphery of said casing below its horizontal center plane,

secondary melting loops in said inductor units operatively connected with said hearth, the melting loop of one of the said inductor units extending through the vertical center plane of the furnace and the melting loops of the other inductor units located at k/each side of said vertical center plane extending through a plane forming an acute angle with said vertical center plane.

3. In a drum-type induction furnace particularly for melting metals turnable about its longitudinal' axis a horizontal hearth, a refractorylined casing housing said hearth, one bottom and two lateral inductor units attached to the circumference of said casing below its horizontal center plane, secondary melting loops in said inductor units operatively connected with said l0 hearth. the melting loop of said bottom inductor unit extending through the longitudinal vertical center plane of the furnace and the melting loops of said lateral inductor units symmetrically located at each side fof said vertical center plane a extending through a plane forming an acute angle with said vertical center plane.

4. In a drum-type induction furnace particularly for melting metals rotatable about its longitudinal center axis a horizontal hearth, a refractory-lined casing housing said hearth, a plurality of inductor units attached to the periphery of said casing below its horizontal center plane, secondary melting loops in said inductor units operatively connected with said hearth and adapted to create an intensied metal ow in and from the same towards the said hearth, the melting loopof one of the said inductor units extending through the vertical center plane of the furnace and the melting loops of the other inductor units located at each side of said vertical center plane extending through a plane forming an acute angle with said vertical center plane.

5. In a drum-type induction furnace particularly for melting metals rotatable about its longitudinal center axis a horizontal hearth, a refractory-lined casing housing said hearth, a plurality of inductor units attached to the periphery of said casing below .its horizontal center plane, secondary melting loops in said inductor units operatively connected with said hearth and adapted to create an intensified unidirectional metal iiow in and from the same towards said hearth, the melting loop of one of said inductor units extending through the vertical center plane of the furnace and the melting loops of the other inductor units located at each side of said vertical center plane extending through a plane forming an acute angle with said vertical center plane.

6. In a drum-type induction furnace particularly for melting metals rotatable about its longitudinal center axis a horizontal hearth, a refractory-lined casing housing said hearth, one bottom and two lateral inductor units attached to the periphery of said casing below its horizontal center plane, secondary melting loops of the twin coil type operatively connected with said hearth, said loops having a channel spaced from said hearth and three substantially straight channels connecting said hearth and said spaced channel, the melting loops of said bottom inductor unit extending through the longitudinal vertical center plane of the furnace and the melting loops of said lateral inductor units symmetrically located at each side 0f said vertical plane extending through a plane forming an. acute angle with said vertical center plane.

'7. In a drum-type induction furnace particularly for melting metals rotatable about its longitudinal center axis a-horizontal hearth, a refractory-lined casing housing said hearth, one bottom and two lateral inductor units attached to the periphery of said casing below its horizontal center plane, secondary melting loops operatively connected with said hearth said loops having a channel spaced from said hearth and substantially straight channels connecting said hearth and said spaced channel, the melting loop of said bottom inductor unit extending through the longitudinal verticalcenter plane of the furnace and the melting loops of said lateral inductor units I symmetrically located at each side of said vertical plane extending through a plane forming an acute angle with said vertical center plane.

8. In a drum-type induction furnace particuits longitudinal center' axis a 'horizontal hearth,

a refractory-lined casing housing said hearth, one bottom and two lateral inductor units replaceably attached to the periphery of said casing below its horizontal center plane, secondary melting loops provided with two identical coil systems operatively connected with said hearth, said loops having a bottom channel spaced from said hearth and three straight channels connecting said hearth and said bottom channel, the melting loop of said bottom inductor unit extending through the longitudinal vertical certer plane of the furnace and the melting loops of each of said Ilateral inductor units symmetrically located at each side of said vertical' plane extending through a plane forming an acute angle with said vertical center plane.

9. In a drum-type induction furnace rotatable about its longitudinal center axis particularly for melting metals a horizontal hearth, a refractorylined casing housing said hearth, one bottom and two lateral inductor units replaceably attached to the periphery of said casing below its horizontal center plane, secondary melting loops having at least two straight melting channels in said inductor units operatively connected with said hearth, the melting loop of said bottom inductor unit extending through the longitudinal vertical center plane of the furnace and the melting loops of said lateral inductor units symmetrically located at each side of said vertical plane extending through a plane forming an acute angle vwith said vertical center plane, the center lines of all melting channels located in the same vertical drum plane converging at one point located above the geometrical center of the furnace.

10. In a drum-type induction furnace particus larly for melting metals rotatable about its longitudinal center axis a horizontal hearth, a refractory-lined casing housing said hearth, one bottom and two lateral inductor units replaceably attached to the periphery of said casing below its horizontal center plane, secondary melt1 ing loops in said inductor units operatively connected with said hearth, the melting loop of said bottom inductor unit extending through the longitudinal vertical center plane of the furnace and the melting loops of said lateral inductor units symmetrically located at each side of said vertical plane extending through a plane forming an acute angle with said vertical center plane, the center planes of the melting loops, of the bottom inductor unit and of a lateral inductor unit forming an vangle between each other of about `45 degrees.

11.` In a4 drum-type induction furnace particularly for melting metals rotatable about its longitudinal center axis a horizontal hearth, a 'refractory-lined casing housing said hearth, one

bottom and two lateral inductor units replaceablyv attached to the circumference of said casing below its horizontal center plane, vsecondary melting loops having at least two straight lateral melting channels in said inductor units operatively connected with said hearth, the melting loop of said bottom said bottom inductor lunit extending through the longitudinal vertical plane of the furnace and the melting loops of said lateral inductor units located at each side of said vertical center plane extending through a plane forming an acute angle with said vertical plane, openings Y in the top portion of said casing in substantial alinement with the center .lines of the melting channels to permit the introduction of cleaning tools into said melting channels from the outside of the furnace.

12. In a drum-type induction furnace particularly `for melting metals rotatable about its longitudinal center axis a horizontal hearth, a refractory-lined casing housing said hearth, a plurality of inductor units replaceably attached to the periphery of said casing below its hormontal cen- 'ter plane,v secondary melting loops in said inductor units, the melting loop of at least one of the said inductor units extending through the vertical center plane of the furnace and the melting loops of the other :Inductor .units located at each side of. said vertical center plane extending through a plane forming. an acute angle with said vertical center plane, an opening in the top portion of said casing, a cover to close said opening, said cover consisting of a plurality of adjacent longitudinally movable sections.

i3. ln a mum-type induction furnace for melting metals mounted to turn about its longitudinal center axis, a horizontal hearth, a plurality of inductor units replaceably attached to the circumference oi? said casing below its horizontal center plane, secondary melting loops in said 1 inductor units the melting loop of at least one of said inductor units extending through the verticai center plane oi the furnace, and the melting loops of the other induotor units located' at each side of said vertical plane extending through a plane forming an acute angle with said vertical center plane, a spigot for the gradual discharge of the metal attached to an end wall of said casa discharge channel in said body having the shape of an inverted V, a discharge channel in said end wall communicating with the inner shank of said V-shaped channel and heating means in the outer portion of said refractory body.

le. In a furnace according to claim 13 an additional opening in an end wall of the furnace casing for the discharge of metal beyond the discharge range of the spigot.

ing to claim 12 the distance between the vortex of the V-shaped channel and the discharge channel in the end-wall of the casing being such as to prevent Vthe outflow of the molten metal from the hearth in the normal working position of the furnace. i

16. In a method of replacing a bottom inductor unit of an inductor furnace according to claim 3 tilting the furnace from the position having the center plane of the melting loop of a bottom inductor unit in alinement with the longitudinal vertical center 'plane of the furnace until said bottom inductor unit arrives in a position where the ycenter plane of its melting loop extends through the horizontal center plane of the furnace, emptying its metal contents into the hearth and exchanging the empty unit for another inductor unit while keeping a lateral inductor unit in operation and nlled with molten metal.

17. In a method of replacing a lateral inductor unit of an induction furnace according to claim v3 rotating the furnacedn either direction from the position having the center plane of the melting loop of a bottom inductor unit in alinement with the longitudinal vertical center plane oi the furnace until a lateral inductor unit arrives in a position where the center plane ofits melting loop substantially extends through the horizontal center plane of the furnace, thereby emptying the metal contents of said inductor unit 15.1111 a drum-type induction furnace accord-Y and a lateral inductor unit in operation and filled with the molten metal 18. In a method for priming the furnace according to claim 3 charging the furnace with metal, tilting the furnace into the lowermost portion of a lateral unit externally preheating the hearth and the inductor units, thereafter introducing molten metal into said lowermost lateral inductor unit, switching the power on the latter, gradually tilting the furnace into its normal operating position and building up the molten bath. i

19. In a furnace according to claim 1 means to shift an exit from the melting loops into the hearth into a section thereof which is substan` tially free from the infiuence of the electromagnetic field produced by said inductor units.

20. In a drum type induction furnace particularly for melting metals a hearth, a refractorylined casing housing said hearth, a plurality of inductor units replaceably attached to the periphery of said casing below its horizontal center plane, secondary melting loops in said inductor units operatively connected with said l hearth, the melting loop of one of thesaid inductor units extending through the vertical center plane of the furnace and the melting loops of the other inductor units located at each side of said lvertical center plane extending through a plane forming an acute angle with said vertical center plane and a current conductive refractory tube inserted into an exit from said secondary melting loops into the hearth, said tube extending into a section of the hearth which is substantially free from the influence of the electromagnetic fleld produced by said inductor units.

21. In a furnace according to claim 7 a current conductive refractory tube inserted with its one end into a connecting channel and radially extending with the other end through the lining of the hearth into a portion of the same which is substantially free from the influence of the electromagnetic fields produced by said inductor units.

22. In a furnace according to claim 6 a current conductive refractory tube inserted with its one end in the central connecting channel and radially extending with the other end through the lining of the hearth into a portion of the same which is substantially free from the influence of the electromagnetic fields produced by said inductor units and passages in the refractory lining of the hearth connecting the lateral connecting channels with the hearth.

23. In a furnace according to claim 6 a cur- A rent conductive refractory tube inserted with its one end in the central connecting channel and radially extending with the other end through the lining of the hearth into a portionl of the same which is substantially free from the influence of the electromagnetic fields produced by said inductor units and passages in the refractory lining of the hearth connecting the lateral connecting channels with the hearth the ilowing kmetal by'metal drawn in the opposite direction into another melting channel of the secondary loop, creating thereby a uniand onedirectional circulation of the melt through the inductor units and the hearth and homogenizing the composition of the metal and the heat distribution in the furnace.

25. In a drum type induction furnace particu- Y larly for melting metals a refractory-lined casing, refractory walls extending through said casing and dividing its inner space into a hearth and lateral chambers, passages in said walls connecting said hearth and said lateral chambers, at least one secondary inductor unit attached to the periphery of said casing, a plurality of melting channels in said unit, at least one melting chan- -nel connected with said hearth and at least one melting channel connected with a lateral chamber.

26. In a drum type induction furnace particularly vfor melting metals a refractory-lined cylindrical casing, vertical refractory walls extending through said casing dividing its inner space into a hearth and two lateral chambers, a charging opening in said casing above said hearth, passages in said walls connecting said hearth and said lateral chambers, at least one secondary inductor unit attached to the circumference of said casing, a plurality of melting channels in said unit, at least one melting channel connected with said hearth and at least one other melting channel connected with each of said lateral chambers.

2'7. In adrum type induction furnace particularly for melting metals a refractory-lined cylindrical casing, two vertical refractory walls extending through said casing and dividing its inner space into a space and two lateral chambers. passages in said walls connecting said hearth with each of the said two chambers, at least one secondary inductor unit attached to the circumference of the bottom portion of said casing, three radially extending melting channels in said inductor unit of which one is a center channel and two are lateral channels, the center channel being connected with said hearth and one lateral channel with one of said chambers.

28. In a drum-type induction furnace particularly for melting metals a refractory-lined cylindrical casing, said casing and dividing its inner space into a hearth and two lateral chambers, passages in said Walls connecting said hearth and said lateral chambers, at least one secondary inductor unit attached to the circumference of said casing, a plurality of melting channels in said unit, a melting channel connected with said hearth and another melting channel connected With a lateral chamber, and means to shift the connection of said melting channel and said hearth into a section of the same which is substantially free from the influence of the electromagnetic field created by said inductor unit and to thereby produce a unidirectional continuous circulation of the molten charge through the hearth, said lateral chambers and said inductor units. i

29; In a drum-type induction furnace particularly for melting metals a refractory-lined cylindrical casing, two vertical refractory walls extending through said casing and dividing its inner space into a hearth and two lateral chambers, passages in said walls connecting said hearth with each of the said two chambers, at least one secondary inductor unit attached to the circumference of the bottom portion of said casing, three refractory walls extending through radial melting channels in said inductor unit of which one is a center channel and two are lateral channels, the center channel being connected with said hearth and one lateral channel with a lateral chamber and means to shift the connection of said center channel and said hearth into a section of the latter which is essentially free from the influence of the electromagnetic eld created by said inductor unit to produce a unidirectional continuous circulation of the molten charge through said hearth, said chambers and said inductor units.

30. In a drum-type induction furnace particularly for melting metals, a refractory-lined cylindrical casing. two vertical refractory walls extending through said casing and dividing its in- A ner space into a hearth and two lateral chambers, passages in said walls connecting said hearth with each of the said two chambers, at least one secondary inductor unit attached to the circumference of the bottom portion of said casing, three radial melting channels in said inductor unit of which one is a center channel and two are lateral channels, the center channel being connected with said hearth and one lateral channel with a lateral chamber and a passage in the refractory lining of said casing extending in alinement with said center channel, shifting the connection between the same and the hearth into a section of the latter which is essentially free from the infiuence of the electromagnetic field created by said inductor unit and a current conductive refractory tube connecting said center channel and said passage. 4

31. In a drum-type induction furnace particularly for melting metals a refractory-lined cylindrical casing, two vertical refractory walls extending through said casing dividing its inner space into a 'hearth and two lateral chambers, passages in said walls connecting said hearth with each of the said two chambers,a charging opening in said casing above said-hearth, at least one secondary inductor unit attached to the circumference below its horizontal center plane of said casing, three radial melting channels in said inductor unit of which one is a center channel and two are lateral channels, the center channel being connected with said hearth and one lateral channel with one lateral chamber, a passage in the refractory lining of said casing extending in alinement with said center channel ending short of the end of the latter and a current conducting refractory tube inserted into the said passage and the said center channel the said passage shifting the connection between said center channel and said heari'fh into a section of the latter which is essentially freelfrom the influence of the electromagnetic eld created by said inductor unit.

32. In a drum-type induction furnace particularly for melting metals a horizontal hearth, a refractory-lined cylindrical casing housing said hearth, two vertical refractory walls extending through said casing dividing its inner space into a hearth and two lateral chambers, passages in said walls connecting said hearth with each of the said two chambers, three secondary inductor units or inductor unit rows attached to the circumference of .said casing beneath its horizontal i6 nection between the same and the hearth into a section of the latter which is substantially free from the inuence of the electromagnetic field produced by said inductor unit, recesses in said refractory lining above the exit of said lateral channels connected therewith and closed towards said hearth and passages in said lining connecting said recesses and the bottom portions of said lateral chambers.

33. In a tiltable drum type induction furnace according to claim 29 the passages in the refractory lining of the drum casing connecting the center channels of the melting loops with the hearth ending short of the. upper exit from the channel and current conductive refractory tubes inserted with their ends into said upper exits from said channels and intovsaid passages.

34. In a drum-type induction furnace a horizontal hearth a refractory-lined'casing housing said hearth, vertical refractory walls extending through said casing dividing its inner space into a hearth and two lateral chambers, passages in said walls connecting the hearth with said chambers, three secondary inductor units replaceably attached to the circumference of the said casing below its horizontal center plane, a plurality of melting channels in said inductor unit, at least one channel connected with each of said chambers.

35. In .a drum-type induction furnace, a hearth a cylindrical refractory-lined casing housing said hearth, two vertical refractory walls extending through said casing and dividing its inner-space into a hearth and two lateral chambers, passages in said walls connecting the hearth with each of said two chambers, a charging opening for said casing above said hearth, three replaceable secondary inductor units attached to the circumference of the bottom portion of said casing, three radial melting channels in said inductor units of which one is a center channel and two are lateral channels, the center channel being connected with said hearth and one lateral channel with each of said lateral chambers.

36. A method of melting metals in a drumtype induction furnace provided with a hearth, a refractory-lined casing housing said hearth and with a plurality of inductor units at its circumference, comprising charging the metal into said hearth, melting the metal by means of the electromagnetic eld produced by said inductor units, conducting the molten metal into lateral refining chambers located in said casing adjacently to said hearth and returning the metal from said chambers to the said inductor units.

37. A method of melting metals in a drumtype induction furnace provided with a hearth and a refractory-lined casing housing said hearth and three inductor units at the circumference thereof, comprising charging the metal into said hearth, melting the metal by means of the electromagnetic field produced by said inductor units, passing the molten metal from said inductorrnnits into a section of the hearth which is practically free from the inuence of the elecltromagnetic field, hereupon conducting the molten metal into lateral refining chambers l0- cated in said casing adjacent to said hearth, returning the metal from said chambers into the said inductor units and creating thereby a unidirectional continuous circulation through the said hearthfsaid lateral chambers and said inductor units. y

38. A method of melting metals in a drumtype induction furnace' provided with a cylinhearth andl at least one inductor unit at the circumference thereof having a. center and two lateral melting channels comprising charging the metal from above into said hearth melting the metalby means of, the electromagnetic fields produced by the said inductor units, passing the molten metal from the center channel of said inductor unit into a section of the hearth which is practically free from the influence of the electromagnetic field,y conducting the metal into lateral refining chambers located in said casing adjacently to said hearth, returning the metal from said chambers into the lateral channels oi the said inductor unit and creating hereby aunidirectional continuous circulation through said hearth, said lateral chambers and said inductorv unit.

39. A method of melting metals in a drumtype induction furnace provided with a substantially cylindrical refractory-lined casing housing a hearth and three inductor units of the twin coil type symmetrically located at the periphery of said casing beneath the horizontal center plane of which one is a central bottom unit and the other ones are lateral units comprising charging metal into said hearth, melting the metal by means of the electromagnetic fields produced by the said inductor units, passing the molten metal from the center channels of said inductor units into a center section of the hearth which is practically free from the influence of the electromagnetic flelds, hereupon conducting the t metal into lateral refining chambers located in of the hearth.

40. In a drum type induction furnace particularly for melting metals a hearth, a refractorylined casing housing said hearth, a plurality of inductor vunit rows attached to the periphery of said casing below its horizontal center plane,

' secondary melting loops in the inductor units operatively connected with said hearth, the melting loops of the inductor units of one row extending through the vertical center plane ofthe furnace and the melting loops of the .inductor units of the other rows located at each side of said vertical center plane extending through a plane forming an acute angle with said vertical center plane.` 4

41. In a drum type induction furnace particularly for melting metals turnable about its longitudinal center axis a hearth, a refractory-lined casing housing said hearth, a plurality of inductor 'unit rows replaceably attached to the periphery 'of said casing below its horizontal center plane, secondary melting loops in said inductor units operatively connected with said hearth, the melting loops of the inductor units of one row extending through the vertical center plane of the kfurnace and the melting loops of the inductor units of the other rows located' at each side of said vertical center plane extending through a plane forming an acute angle with said vertical centerplane.

42. In a drum type induction furnace particularly foil melting metals turnable about its longitudinal axis a horizontal hearth, 'a refractorytwo lateral inductor unit rows attached to the circumference of said casing below its horizontal center plane, secondary melting loops in the inductor units operatively connected with said hearth, the melting loops of the bottom inductor unit row extending through the longitudinal vertical center plane of the furnace and the melting loops of the two lateral inductor unit rows symmetrically located at each side or' said vertical center plane extending tnrougn a plane forming an acute angle with said vertical center plane.

43. In a drum type induction furnace particularly for melting metals rotatable about its longitudinal center axis a horizontal hearth, a refractory-lined casing housing said hearth, a plurality of inductor unit rows attached to the periphery of said casing below its horizontal center piane, secondary melting loops in said inductor umts operatively connected with said hearth and adapted to create an intensified metal flow in and from the same towards .the said hearth, the melting loops of the inductor units of one row extending through the vertical center 'plane of the furnace and the melting loops of the inductor unit of the other rows located at each side of said vertical center plane extending through a. plane forming an acute angle with said vertical center plane.

44. In a drum type induction furnace particularly for melting metals rotatable about its longitudinal center axis a horizontal hearth, a refractory-lined casing housing said hearth, a plurality of inductor unit rows attached to the periphery of said casing below its horizontal center plane, secondary melting loops in said inductor units operatively connected with said hearth and adapted to create an intensied unidirectional metal flow in and from the same towards said hearth, the melting loops of the inductor units of one row extending through the vertical center plane of the furnace and the melting loops of the inductor units of the other rows located at each side of said vertical center plane extending through a plane forming an acute angle with said vertical center plane.

45. In a drum type induction furnace particularly for melting metals rotatable about its longitudinal center axis a horizontal hearth, a refractory-lined casing housing said hearth, one bottom and two lateral inductor unit rows attached to the periphery of said casing below its horizontal center plane, secondary melting loops of the twin coil type including two identical coil arrangements operatively connected with said hearth, said loops having a channel spaced from said hearth and three substantially straight channels connecting said hearth and said spaced channel, the melting loops of the bottom inductor unit row extending throughthe longitudnal vertical center plane of the furnace and the melting loops of the two lateral inductor unit rows symmetrically located at each side of said vertical plane extending through a plane forming an acute angle with said vertical center plane.

46. In a drum'type induction furnace particularly for melting metals rotatable about its longitudinal center axis a horizontal hearth, a refractory-lined casing housing said hearth, one bottom and two lateral inductor unit rows attached to the periphery of said casing below its horizontal center plane, secondary melting loops operatively connected with said hearth said loops having a channel spaced from said hearth and substantially straight channels connecting said hearth and said spaced channel, the melting loops of the inductor units in the bottom row extending through the longitudinal vertical center plane of the furnace and the melting loops of the two lateral inductor unit rows symmetrically located at each side of said vertical plane extending through a plane forming an acute angle with said vertical center plane.

47. In a drum type induction furnace particularly for melting metals which is rotatable about its longitudinal center axis a horizontal hearth, a refractory-lined casing housing said hearth, one bottom and two lateral inductor unit rows replaceably attached to the periphery of said casing below its horizontal center plane, secondary melting loops of the twin-coil type operatively connected with said hearth, said loops having a bottom channel spaced from said yhearth and three straight channels connecting said hearth and said bottom channel, the melting loops of the inductor units of the bottom row extending through the longitudinal vertical center plane of the furnace and the melting loops of each of the two lateral inductor unit rows symmetrically located at each side of said vertical plane extending through a plane forming an acute angle with said vertical center plane.

48. In a drum type induction furnace rotatable about its longitudinal center axis particularly for melting metals a horizontal hearth, a refractorylined casing housing said hearth, one bottom and two lateral inductor unit rows replaceably attached to the periphery of said casing below its horizontal center plane, secondary melting loops having at least two straight melting channels in said inductor units operatively connected with said hearth, the melting loops of the inductor units in the bottom row extending through thel longitudinal vertical center plane of the furnace and the melting loops of the two lateral inductor unit rows symmetrically located at each side of said vertical plane extending through a lplane forming an acute angle with said vertical center plane, the center lines of all melting channels located in the same vertical 'drum plane converging at one point located above the geometrical center of the furnace.

49. In a drum type induction furnace particu- 'larly for melting metals rotatable about its longitudinal center axis a horizontal hearth, a refractory-lined casing housing said hearth, one bottom and two lateral inductor unit rows replaceably attached to the periphery of said casing below its horizontal center plane, secondary melting loops in said inductor units operatively connected with said hearth, the melting loops of the inductor units in the bottom row extending through the longitudinal vertical center plane of the furnace and the melting loops of the two lateral inductor unit rows symmetrically located at each side of said vertical planeA extending through a plane forming an acute angle with said vertical center plane, the center planes of the I melting loops of the bottom inductor unit rows and of a lateral inductor unit row forming an angle between each other of about 45 degrees.

50. In a drum type induction furnace particu-.

loops of the inductor units in the bottom row extending through the longitudinal vertical plane of the furnace and the melting loops of the two lateral inductor unit rows located at each side of said vertical center plane extending through aplane forming an acute angle with said vertical plane, openings in the top portion of said casing in substantial alignment with the center lines of the melting channels to permit the introduction of cleaning tools into said melting channels from the outside of the furnace.

51. In a drum type induction furnace particularly for melting metals rotatable about its longitudinal center axis a horizontal hearth, a refractory-lined casing housing said hearth, a plurality of inductor unit rows replaceably attached to the periphery of said casing below its horizontal center plane, secondary melting loops in said inductor units, the melting loops of at least one of the inductor units of said rows extending through the y vertical center plane of the furnace and the melting loops ofthe inductor units in the other rows located at each side of said vertical center plane extending through a plane forming an acute angle with said vertical center plane, an opening in the top portion of said casing. a cover to close said opening, said cover consisting of a plurality of adjacent longitudinally movable sections.

52. In a drum type induction furnace for meltlng metals mounted to turn about its longitudinal center axis, a horizontal hearth, a plurality of in= ductor unit rows replaceably attached to the circumierence of said casing below its horizontal center plane, secondary melting loops in said inductor units the melting loops of the inductor units of at least one row extending through the vertical center plane of the furnace, and the melting loops of the other inductor unit rows located at each side of said vertical plane ex-` tending through a plane forming an acute angle with said vertical center plane, a spigot for the gradual discharge of the metal attached to an end wall of said casing, said spigot consisting of a refractory body, a discharge channel in said body having the shape of an inverted V, a discharge channel in said end wall communicating with the inner shank of said V-shaped channel and heating means in the outer portion of said refractory body.

53. In a furnace according to claim y52 an additional opening in an end wall of the furnace casing for the discharge of metal beyond the discharge range of the spigot.

54. In 'a drum type induction furnace according to claim 52 the distance between the vortex of the V-shaped channel and the discharge channel in the end-wall of the casing being such as to prevent the outflow of the molten metal from the hearth in the normal working position of the furnace.

55. In a method of replacing a. bottom inductor unitof an inductor furnace ,according to claim 42 tilting the furnace from the position having the center plane of the melting loops of the bottom inductor unit row in alignment with the longitudinal vertical center plane of the furnace untilsaid bottom inductor unit row arrives in a position where the center planes of its melting loops extends through the horizontal center f plane of the furnace, emptying its metal contents 21- l unit of an induction furnace according to claim 42 rotating the furnace in either direction from the position having the center plane of the melting loops of the bottom inductor unit row in alignment with the longitudinal vertical center plane of the furnace until a lateral inductor unit row arrives in a position where the center planes of its melting loops substantially extend through the horizontal center plane of the furnace, emptying the metal contents of the inductor units of said row into the hearth and exchanging an inductor unit for another inductor unit while keeping the bottom and the other lateral inductor unit rows in operation and filled with the molten metal.

57. In a method for priming the furnace according to claim 42 charging the furnace with metal tilting the furnace into the lowermost portion of a lateral unit row, externally preheating the hearth and the inductor unit rows, thereafter introducing molten metal into the inductor units of said lowermost lateral inductor unit row, switching the power on the latter, gradually tilting the furnace into its normal operating position and building up the molten bath.

58. In a furnace according to claim 40 means to shift the refractory conduits exit from the melting loops of the inductor unit rows into the hearth into a section thereof which is substantially free from the influence of the electromagnetic field produced by said inductor units.

59. In a drum type induction furnace particularly for melting metals a hearth, a refractorylined casing housing said hearth, a plurality of inductor unit rows replaceably attached to the periphery of said casing below its horizontal center plane, secondary melting loops in said inductor units operatively connected with said hearth, the melting loops of the said inductor units of one row extending through the vertical center plane of the furnace and the melting loops of the inductor units of the other rows located at each side of said vertical center plane extending through a plane forming an acute angle with said vertical center plane and current conductive refractory conduits inserted into an exit from the secondary melting loops into the hearth, said conduits extending into a section of the hearth which is substantially free from the influence of the electromagnetic field produced by said inductor units.

60. In a furnace according to claim 46 current conductive refractory tubes inserted with the one end into a connecting channel and radially exy tending with the other end through the lining of the hearth into a portion of the same which is substantially free from the influence of the electromagnetic fields produced by the inductor units.

61. In a furnace according to claim 45 current conductive refractory tubes inserted with the one end in the central connecting channels and radially extending with the other end through the lining of the hearth into a portion of the same which is substantially free from the influence of the electromagnetic fields produced by the inductor units and passages in the refractory lining of the hearth connecting the lateral connecting channels with the hearth.

62. In a furnace according to claim 45 current conductive refractory tubes inserted with the one end in the central connecting channel and radially extending with the other end through the lining of the hearth into a portion of the same which is substantially free from the influence of the electromagnetic fields produced by the in- 22 ductor units and passages in the refractory lining of the hearth connecting the lateral connecting channels with the hearth the cross section of the said passages increasing towards the said channels.

63. The method of melting metals in a furnace according to claim 59 forcing the melt to flow by the internal pressure produced by the electromagnetic eld from a melting channel through its current conductive refractory conduits into a portion of the hearth which is practically free from the influence of the field, replacing the outflowing metal by metal drawn in the opposite direction into another melting channel of said melting loop, creating thereby a uniand onedirectional circulation of the rnelt through the inductor unit rows and the hearth and homogenizing the composition of the metal and the heat distribution in the furnace.

64. A method of melting metals in a drumtype induction furnace provided with a hearth, a refractory-lined casing housing said hearth and with a plurality of inductor unit rows at its circumference, comprising charging the metal into said hearth, melting the metal by means of the electromagnetic eld produced by said inductor unit rows, conducting the molten metal into lateral refining chambers located in said casing adj acently to said hearth and returning the metal from said chambers to the said inductor unit rows.

65. In a drum type induction furnace particularly for melting metals a hearth, a refractorylined casing housing said hearth, a plurality of inductor units attached to the periphery of said casing below its horizontal center plane, secondary melting loops in said inductor units operatively connected with said hearth, the melting loop of one of the said inductor units extending through the vertical center plane of the furnace and the melting loops of the other inductor units located at each side of said vertical center plane extending through a plane forming an acute angle with said vertical center plane and a closeable. door located at the top level of the molten bath for the removal of slags from the surface of the bath.

66. In a drum type induction furnace particularly for melting metals a hearth, a refractorylined casing housing said hearth, a plurality of inductor unit rows attached to the periphery of said casing below its horizontal center plane, secondary melting loops in said inductor units operatively connected with said hearth, the melting loops of one or' the said inductor unit rows extending through the vertical center plane of the furnace and the melting loops of the inductor rows of the other units located at each side of said vertical center plane extending through'a plancforming an acute angle with said vertical center plane and a closeable door located at the top level of the molten bath for the removal of slags from the surface of the bath.

67. ln a tiltable drum type induction furnace particularly for melting metals rotatable about its longitudinal center axis a horizontal hearth, a refractory-lined casing housing said hearth, one bottom and two lateral inductor unit rows attached to the periphery of said casing below its horizontal center plane, secondary melting loops of the twin coil type operatively connected with said hearth, said loops having a channel spaced from said hearth and three substantially straight channels connecting said hearth and said spaced channel, the melting loop of said bottom inductor unit rows extending through the longitudinal vertlcalcenter plane of the furnace and the melting loops of said lateral inductor unit rows symmetrically located at each side of said vertical plane extending through a plane forming an acute angle with said vertical center plane, passages in the refractory lining of the hearth connecting the. lateral channels with the hearth and plugs to close the entrance end of these passages into the hearth.'

MARIO TAMA.

REFERENCES CETED The'i'following references are of record in the le-'ofthis patent:

UNITED STATES PATENTS Nniber Name Date Re. 18,3162 De Zubilia Feb. 23, 1932 Re.22,602 Tama. Feb. 13, 1945 i6 Number.

Name Date Unger Apr. 26, 1927 Weed Nov. 8, 1927 Gross July 10, 1928 Russ Feb. 17, 1931 Case Sept. 11, 1934 Summey Dec. 14, 1937 Strube et al July 18, 1939 Tama 'et al June 9, 1942 Tama et al. Jan. 30, 1945 Tama et al.. July 15, 1947 Tama et al". June 28, 1949 FORMGH PATENTS Country Date Germany Mar. 8, 1937 Sweden'.- Sept. 2, 1893 Sweden Apr. 29, 1942 

